This invention relates to a process for the fabrication of a semiconductor integrated circuit device, particularly to a technique effective when applied to gate processing of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a poly-metal gate.
Japanese Patent Application Laid-Open No. H5-152282 (which will hereinafter be called xe2x80x9cOhmixe2x80x9d), dicloses an oxide film forming device for oxidizing a semiconductor wafer, or the like, with water synthesized using a catalyst, such as nickel.
On pages 128-133 of Papers of the Lecture addressed at the 45-th Symposium of Semiconductor Integrated Circuit Technique held on Dec. 1-2, 1992 (which will hereinafter be called xe2x80x9cNakamuraxe2x80x9d), oxide film formation under a strong reducing atmosphere, which contains water vapor synthesized by a stainless catalyst is disclosed.
Japanese Patent Application Laid-Open No. S59-132136 (which will hereinafter be called xe2x80x9cKobayashixe2x80x9d), discloses a process, in a silicon semiconductor integrated circuit device having a refractory metal (high-melting point metal) gate, for carrying out auxiliary thermal oxidation (which will hereinafter be called xe2x80x9clight oxidationxe2x80x9d or xe2x80x9cauxiliary oxidation after gate formationxe2x80x9d) not of the gate metal itself, but necessary portions other than the gate metal, under a mixed atmosphere of water vapor and hydrogen after gate patterning, thereby adjusting an insulation film at the periphery below the gate.
Similarly, Japanese Patent Application Laid-Open No. H3-119763 (which will hereinafter be called xe2x80x9cKatadaxe2x80x9d) and Japanese Patent Application Laid-Open No. H7-94716 (which will hereinafter be called xe2x80x9cMuraokaxe2x80x9d), discloses a process for forming a gate having a three-layered structure made of tungsten, titanium nitride and polysilicon, and then subjecting it to oxidation treatment under a mixed atmosphere of hydrogen, water vapor and nitrogen.
It is presumed that for a device having a circuit formed of a minute MOSFET, whose gate length is 0.25 xcexcm or smaller, such as a DRAM (Dynamic Random Access Memory) of the type available since the development of the 256 Mbit (megabit) memory, a gate processing step using a low-resistance conductive material including a metal film will become indispensable to reduce the parasitic resistance of a gate electrode.
As such a low-resistance gate electrode material, so-called poly-metal (which generally means a refractory metal formed directly or indirectly over a polycrystalline silicon electrode) having a refractory metal film stacked over a polycrystalline silicon film is regarded as promising. The poly-metal can be used not only as a gate electrode material, but also as an interconnection material because it has a sheet resistance as low as 2 xcexa9/xe2x96xa1. According to an investigation by the present inventors, W (tungsten) Mo (molybdenum), Ti (titanium) or the like, which exhibits a good low resistance even in a low temperature process not higher than 800xc2x0 C. and has a high electro-migration resistance, can be used as the refractory metal. Since the stacking of such a refractory metal film directly on a polycrystalline silicon film lowers the adhesion between these two films or tends to form a high-resistance silicide layer at the interface between these two films by a high-temperature heat treatment process, the poly-metal gate is practically formed of a three-layered structure having, between the polycrystalline silicon film and the refractory metal film, a barrier layer made of a metal nitride film, such as TiN (titanium nitride) or WN (tungsten nitride).
Based on an investigation by the present inventors, gate processing is conventionally carried out as follows. First, a semiconductor substrate is thermally oxidized to form a gate oxide film on its surface. Although a thermally oxidized film is generally formed in a dry oxygen atmosphere, wet oxidation is employed for the formation of a gate oxide film because the defect density in the film can be reduced. In wet oxidation, a pyrogenic method is employed in which water is formed by the combustion of hydrogen in an oxygen atmosphere and then fed to the surface of a semiconductor wafer together with oxygen.
The pyrogenic method, however, is accompanied with the drawback that combustion is effected by igniting hydrogen jetted from a nozzle attached to the tip of a quartz-made hydrogen gas inlet tube, but heat generated upon combustion melts the nozzle and generates particles, which presumably become a contamination source for the semiconductor wafer. For the formation of water, therefore, a method using a catalyst without combustion also has been proposed.
The above-described Ohmi publication discloses a thermal oxidation apparatus having a hydrogen gas inlet tube formed at its inside from Ni (nickel) or a Ni-containing material and is equipped with means for heating the hydrogen gas inlet tube. In this thermal oxidation apparatus, Ni (or a Ni-containing material) inside of the hydrogen gas inlet tube heated at 300xc2x0 C. or higher is brought into contact with hydrogen to generate a hydrogen activated species and then, the hydrogen activated species is reacted with oxygen (or an oxygen-containing gas), whereby water is generated. Water is thus generated in such a catalytic manner without combustion so that neither melting of the quartz-made hydrogen gas inlet tube at its tip point nor generation of particles occurs.
Over the gate oxide film formed by such a wet oxidation method, a gate electrode material is deposited, followed by patterning of the gate electrode material by dry etching with a photoresist as a mask. After the photoresist is removed by ashing treatment, the dry etching residue or ashing residue on the surface of the substrate is removed using an etching solution, such as hydrofluoric acid.
By the above-described wet etching, the gate oxide film in a region other than that below the gate electrode is etched and, at the same time, the gate oxide film at the side wall end portions of the gate electrode are etched isotropically and undercuts are formed, which brings about inconveniences, such as lowering in pressure resistance of the gate electrode. With a view to improving the profile having undercuts formed at the side-wall end portions of the gate electrode, the substrate is subjected to light oxidation treatment, that is, it is subjected to thermal oxidation again to form an oxide film on its surface.
The above-described refractory metals, such as W and Mo, are considerably prone to oxidation under a high-temperature oxygen atmosphere so that the application of the above light oxidation treatment to a gate electrode of a poly-metal structure oxidizes the refractory metal film, thereby increasing its resistance or partially peeling off the film from the substrate. In the gate processing using a poly-metal, it is therefore necessary to take countermeasures against the oxidation of a refractory metal film upon light oxidation treatment.
The above-described Kobayashi publication discloses a technique of selectively oxidizing Si without oxidizing a W (Mo) film by forming over a Si (silicon) substrate a gate electrode of a W- or Mo-film-containing poly-metal structure and then carrying out light oxidation in a mixed atmosphere of water vapor and hydrogen. This technique makes use of the difference between W (or Mo) and Si in a water vapor/hydrogen partial pressure ratio which brings about equilibrium in redox reaction. In this technique, selective oxidation of Si is realized by setting the partial pressure ratio within a range where W (or Mo) once oxidized by water vapor is reduced rapidly by coexisting hydrogen, but Si remains oxidized. The mixed atmosphere of water vapor and hydrogen is generated by the bubbling system which feeds hydrogen gas in pure water carried in a container and the water vapor/hydrogen partial pressure ratio is controlled by changing the temperature of the pure water.
The above-described Katada and Muraoka publication disclose a technique of forming a gate electrode of a poly-metal structure, more specifically, forming a metal nitride film such as TiN and a metal film such as W on a Si substrate through a gate oxide film, and then carrying out light oxidation in an atmosphere obtained by diluting a reducing gas (hydrogen) and an oxidizing gas (water vapor) with nitrogen. According to this, only Si can be oxidized selectively without oxidation of the metal film. At the same time, oxidation of the metal nitride film can be prevented, because denitrifying reaction from the nitride metal film can be prevented by diluting the water vapor/hydrogen mixed gas with nitrogen.
As described above, in the step of forming a gate electrode of a poly-metal structure, it is effective for an improvement in the pressure resistance of a gate oxide film and oxidation prevention of a metal film, to carry out light oxidation in a water vapor/hydrogen mixed gas having a predetermined partial pressure.
The conventional bubbling method, which has been proposed as a method for forming the water vapor/hydrogen mixed gas, is accompanied with the drawback that since the water vapor/hydrogen mixed gas is generated by supplying a hydrogen gas into pure water charged in advance in a container, foreign matters mixed in pure water is fed to an oxidizing furnace together with the water vapor/hydrogen mixed gas and presumably contaminates the semiconductor wafer.
The bubbling method is also accompanied with other drawbacks in that, since the water vapor/hydrogen partial pressure is controlled by changing the temperature of pure water, (1) the partial pressure ratio varies easily and the optimum pressure ratio cannot be attained with high precision, and (2) a water vapor concentration on the order of ppm cannot be attained owing to the controllable range of the water vapor concentration, which is as narrow as several to ten-odd %.
As will be described later, in the redox reaction of Si or a metal by using a water vapor/hydrogen mixed gas, oxidation tends to proceed faster when the water vapor concentration is higher. When Si is oxidized at a comparatively high water vapor concentration as the water vapor/hydrogen mixed gas formed by the bubbling system, the oxide film grows in a markedly short time owing to a high oxidation rate. A minute MOSFET having a gate length not greater than 0.25 xcexcm is required to have a gate oxide film as thin as 5 nm or less in order to maintain the electrical properties of the device. Accordingly, it is difficult to form such a ultra-thin gate oxide film uniformly and with good controllability if the water vapor/hydrogen mixed gas generated by the bubbling method is used. When oxidation is carried out at a low temperature (for example, 80xc2x0 C. or lower) to reduce the growth rate of the oxide film, a gate oxide film having good quality cannot be obtained.
An object of the present invention is to provide a technique which prevents, in gate processing by using a poly-metal, the oxidation of a metal film upon light oxidation treatment after patterning of a gate electrode and makes it possible to control reproducibility of the oxide film formation and homogeneity of the oxide film thickness at side wall end portions of the gate electrode.
The above and other objects and novel features of the present invention will become apparent from the following description thereof and the accompanying drawings.
Among the features disclosed in the present application, typical ones will be summarized briefly as follows:
(1) A process for the fabrication of a semiconductor integrated circuit device according to the present invention comprises depositing a conductive film including at least a metal film over a gate oxide film formed on the principal surface of a semiconductor substrate and patterning the conductive film to form a gate electrode for a MOSFET; and feeding a hydrogen gas containing water vapor generated from hydrogen and oxygen by catalytic action to the principal surface of the semiconductor substrate heated to a predetermined temperature or vicinity thereof to selectively oxidize the principal surface of the semiconductor substrate, thereby improving a profile of side-wall end portions of the gate electrode.
(2) In the above process, the conductive film includes at least a W film or a Ti film.
(3) In the above process, the water vapor/hydrogen partial pressure ratio of the water-vapor-containing hydrogen gas is set within a range reducing the metal film and oxidizing the principal surface of the semiconductor substrate.
(4) In the above process, the conductive film contains at least a Ti film and the principal surface of the semiconductor substrate is selectively oxidized using hydrogen gas which contains water vapor at a concentration low enough to suppress deterioration of the gate electrode due to oxidation of the Ti film to the minimum.
(5) In the above process, the conductive film includes at least a W film and the principal surface of the semiconductor substrate is selectively oxidized using hydrogen gas which contains water vapor at a concentration low enough to permit the control of oxidation rate and oxide film thickness.
(6) A process for the fabrication of a semiconductor integrated circuit device according to the present invention comprises depositing a conductive film including at least a metal film over a gate oxide film, which has been formed on the principal surface of a semiconductor substrate to have a film thickness not greater than 5 nm, and patterning the conductive film to form a gate electrode for a MOSFET; and feeding hydrogen gas containing water vapor, which has been formed from hydrogen and oxygen by catalytic action, at a concentration low enough to permit the control of reproducibility of oxide film formation and homogeneity of an oxide film thickness to the principal surface of the semiconductor substrate heated to a predetermined temperature or vicinity thereof to selectively oxidize the principal surface of the semiconductor substrate, thereby improving a profile of side-wall end portions of the gate electrode.
(7) A process for the fabrication of a semiconductor integrated circuit device according to the present invention comprises the following steps (a) to (d):
(a) thermally oxidizing a semiconductor substrate to form over the principal surface thereof a gate oxide film and then depositing a conductive film containing at least a metal film over the gate oxide film;
(b) patterning the conductive film by dry etching with a photoresist film as a mask to form a gate electrode for a MOSFET;
(c) wet etching the principal surface of the semiconductor substrate after removal of the photoresist film; and
(d) setting a water vapor/hydrogen partial pressure ratio of a hydrogen gas containing water vapor generated from hydrogen and oxygen by catalytic action within a range which reduces the metal film and oxidizes the principal surface of the semiconductor substrate, and selectively oxidizing the principal surface of the semiconductor substrate by feeding the water-vapor-containing hydrogen gas to the principal surface of the semiconductor substrate heated to a predetermined temperature or the vicinity thereof, thereby improving a profile of side-wall end portions of the gate electrode impaired by the wet etching.
(8) In the above process, the conductive film is made of a polycrystalline silicon film, a metal nitride film deposited over the polycrystalline silicon film and a metal film deposited over the metal nitride film.
(9) In the above process, the metal nitride film is made of WN or TiN, while the metal film is made of W, Mo or Ti.
(10) In the above process, the gate electrode has a gate length not greater than 0.25 xcexcm.
(11) In the above process, the gate electrode is a gate electrode of a MISFET for memory cell selection which constitutes a memory cell of a DRAM.
(12) In the above process, the semiconductor substrate is heated at 800 to 900xc2x0 C.
(13) In the above process, the principal surface of the semiconductor substrate is selectively oxidized by a single-wafer-process system.
(14) In the above process, the principal surface of the semiconductor substrate is selectively oxidized by batch treatment.
Other aspects of the present invention will next be described by the item:
1. A process for the fabrication of a semiconductor integrated circuit device comprising the following steps:
(a) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film made mainly of tungsten over the polysilicon film directly or through a barrier layer;
(c) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to additional thermal oxidation treatment under a mixed atmosphere containing a hydrogen gas and water vapor synthesized from oxygen and hydrogen gases by a catalyst.
2. A process as described under item 1 above, wherein the barrier layer contains a tungsten nitride film.
3. A process as described under item 2 above, wherein the step (d) is carried out under conditions which do not substantially oxidize the refractory metal film and the barrier layer.
4. A process as described under item 3 above, wherein the gate insulation film contains a silicon oxide nitride film.
5. A process for the preparation of a semiconductor integrated circuit device, which comprises the following steps:
(a) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film over the polysilicon film directly or through a barrier layer;
(c) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to additional thermal oxidation treatment under a mixed atmosphere containing a hydrogen gas and water vapor synthesized from oxygen and hydrogen gases by a catalyst.
6. A process as described under item 5 above, wherein a barrier layer is provided.
7. A process as described under item 6 above, wherein the step (d) is carried out under conditions which do not substantially oxidize the refractory metal film and the barrier layer.
8. A process for the fabrication of a semiconductor integrated circuit device, which comprises the following step:
(a) carrying out heat treatment to oxidize, between a first region and a second region being made of a material different from that of the first region, each over a semiconductor wafer, the first region under a mixed atmosphere containing a hydrogen gas and water vapor synthesized from oxygen and hydrogen gases by a catalyst without substantially oxidizing the second region.
9. A process as described under item 8 above, wherein the first region is a part of the wafer itself.
10. A process as described under item 9 above, wherein the second region is a thin film formed directly or indirectly over the surface of the wafer.
11. A process for the fabrication of a semiconductor integrated circuit device, which comprises following steps:
(a) forming a first film made mainly of silicon over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film over the polysilicon film directly or through a barrier layer;
(c) forming a gate electrode by patterning the first film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to additional thermal oxidation treatment under a mixed atmosphere containing a hydrogen gas and water vapor synthesized from oxygen and hydrogen gases by a catalyst.
12. A process as described under item 11 above, wherein the step (d) is carried out under conditions for not substantially oxidizing the refractory metal film.
13. A process for the fabrication of a semiconductor integrated circuit device, which comprises the following steps:
(a) forming, on the silicon surface of a semiconductor wafer, a groove for element isolation;
(b) embedding the groove for element isolation with an embedding material from outside;
(c) flattening the surface of the wafer by chemical mechanical polishing subsequent to the step (b);
(d) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of the semiconductor wafer;
(e) forming a refractory metal film over the polysilicon film directly or through a barrier layer;
(f) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(g) subsequent to the step (f), subjecting the silicon and polysilicon portions to thermal oxidation treatment without substantially oxidizing the refractory metal film under a mixed atmosphere containing a hydrogen gas and water vapor.
14. A process as described under item 13 above, wherein the barrier layer contains a nitride film of the refractory metal.
15. A process as described under item 14 above, wherein the refractory metal is tungsten.
16. A process for the fabrication of a CMOS semiconductor integrated circuit device, which comprises the following steps:
(a) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film made mainly of tungsten over the polysilicon film directly or through a barrier layer containing a tungsten nitride film;
(c) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to thermal oxidation treatment without substantially oxidizing the refractory metal film under a mixed atmosphere containing a hydrogen gas and water vapor.
17. A process for the fabrication of a CMOS semiconductor integrated circuit device, which comprises the following steps:
(a) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film made mainly of tungsten over the polysilicon film through a barrier layer containing a tungsten nitride film;
(c) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to thermal oxidation treatment without substantially oxidizing the refractory metal film under a mixed atmosphere of gases oxidative and reductive to silicon and polysilicon.
18. A process for the fabrication of a semiconductor integrated circuit device, which comprises the following steps:
(a) forming a polysilicon film over a silicon-oxide-film-containing gate insulation film formed over the silicon surface of a semiconductor wafer;
(b) forming a refractory metal film made mainly of tungsten over the polysilicon film directly or through a barrier layer;
(c) forming a gate electrode by patterning the polysilicon film and the refractory metal film; and
(d) subsequent to the step (c), subjecting the silicon and polysilicon portions to additional thermal oxidation treatment without substantially oxidizing the refractory metal film under a mixed atmosphere of a gas reductive to silicon and polysilicon and an oxidizing gas synthesized by a catalyst oxidative to silicon and polysilicon.
19. A process as described under item 18 above, wherein the barrier layer contains a tungsten nitride film.
20. A process as described under item 19 above, wherein the gate insulation film contains a silicon oxide nitride film.
Other features of the present invention will next be described by item as follows.
21. A process for the fabrication of a semiconductor integrated circuit, which comprises depositing a conductive film containing at least a metal film over a gate oxide film formed on the principal surface of a semiconductor substrate and then forming a gate electrode for MOSFET by patterning the conductive film; and supplying a hydrogen gas containing water vapor formed from hydrogen and oxygen by catalytic action to the principal surface of the semiconductor substrate heated at a predetermined temperature or the vicinity thereof and selectively oxidizing the principal surface of the semiconductor substrate, thereby improving a profile of side-wall end portions of the gate electrode.
22. A process as described under item 21 above, wherein the conductive film contains at least a W film or Ti film.
23. A process as described under item 21 above, wherein a water vapor/hydrogen partial pressure ratio of the water-vapor-containing hydrogen gas is set within a range which reduces the metal film and oxidizes the principal surface of the semiconductor substrate.
24. A process as described under item 21 above, wherein the conductive film contains at least a Ti film and the principal surface of the semiconductor substrate is selectively oxidized using a hydrogen gas which contains water vapor at a concentration low enough to suppress deterioration of the gate electrode owing to the oxidation of the Ti film to the minimum.
25. A process as described under item 21 above, wherein the conductive film contains at least a W film and the principal surface of the semiconductor substrate is selectively oxidized using a hydrogen gas which contains water vapor at a concentration low enough to permit control of the oxidizing rate and oxide film thickness.
26. A process for the fabrication of a semiconductor circuit device, which comprises depositing a conductive film containing at least a metal film over a gate oxide film which has been formed on the principal surface of a semiconductor substrate to have a film thickness not greater than 5 nm and then forming a gate electrode for a MOSFET by patterning the conductive film; and supplying a hydrogen gas which contains water vapor, formed from hydrogen and oxygen by catalytic action, at a concentration low enough to permit the control of reproducibility of oxide film formation and homogeneity of oxide film thickness to the principal surface of the substrate heated at a predetermined temperature or the vicinity thereof and selectively oxidizing the principal surface of the semiconductor substrate, thereby improving a profile of side-wall end portions of the gate electrode.
27. A process for the fabrication of a semiconductor integrated circuit, which comprises the following steps (a) to (d):
(a) thermally oxidizing a semiconductor substrate to form a gate oxide film on the principal surface of the substrate and then depositing a conductive film containing at least a metal film over the gate oxide film;
(b) patterning the conductive film by dry etching using a photoresist film as a mask, thereby forming a gate electrode for a MOSFET;
(c) removing the photoresist film and then wet etching the principal surface of the semiconductor substrate; and
(d) setting a water vapor/hydrogen partial pressure ratio of a hydrogen gas containing water vapor generated from hydrogen and oxygen by catalytic action within a range which reduces the metal film and oxidizes the principal surface of the semiconductor substrate, and selectively oxidizing the principal surface of the semiconductor substrate by feeding the water-vapor-containing hydrogen gas to the principal surface of the semiconductor substrate heated at a predetermined temperature or the vicinity thereof, thereby improving the profile of side-wall end portions of the gate electrode impaired by the wet etching.
28. A process as described under item 27 above, wherein the conductive film is made of a polycrystalline silicon film, a metal nitride film deposited over the polycrystalline silicon film, and a metal film deposited over the metal nitride film.
29. A process as described under item 28 above, wherein the metal nitride film is made of WN or TiN, while the metal film is made of W, Mo or Ti.
30. A process as described under item 27 above, wherein the gate electrode has a gate length not greater than 0.25 xcexcm.
31. A process as described under item 27 above, wherein the gate electrode is a gate electrode of a MISFET for the memory cell selection which constitutes a memory cell of a DRAM.
32. A process as described under item 27 above, wherein the semiconductor substrate is heated at 800 to 900xc2x0 C.
33. A process as described under item 27 above, wherein selective oxidation of the principal surface of the semiconductor substrate is carried out by a single-wafer-process system.
34. A process as described under item 27 above, wherein selective oxidation of the principal surface of the semiconductor substrate is carried out by batch treatment.
Effects available by the typical aspects and features, among the embodiments disclosed in the present application, will next be described briefly.
According to the present invention, in gate processing using a poly-metal, oxidation of a metal film at the time of light oxidation treatment subsequent to gate patterning can be prevented and, at the same time, the reproducibility of oxide film formation and the homogeneity of the oxide film thickness at the side wall end portions of a gate can be controlled favorably. In particular, an ultra-thin gate oxide film which has a film thickness not greater than 5 nm, which has improved pressure resistance and a high quality, can be formed with a uniform thickness and good reproducibility, which brings about an improvement in the reliability and production yield of a device which has a circuit formed of a fine MOSFET having a gate length of 0.25 xcexcm or less.